TW201521898A - Method of producing cold-worked centrifugal cast composite tubular products - Google Patents

Abstract

A method of producing a seamless, composite tubular product includes centrifugally casting a metal or alloy into a tubular workpiece having an inner diameter. The method then centrifugally casts a corrosion resistant alloy in the inner diameter of the tubular workpiece to form a composite tubular workpiece having an inner diameter and an outer diameter. The inner diameter of the composite tubular workpiece is formed of the corrosion resistant alloy, and the outer diameter is formed of the metal or alloy. The method then subjects the composite tubular workpiece to at least about a 25% wall reduction at a temperature below a recrystallization temperature of the workpiece using a metal forming process. The metal forming process includes radial forging, rolling, pilgering, and/or flowforming.

Description

Method for manufacturing a cold-processed centrifugally cast composite tubular product [Cross-reference to related applications]

This application is a continuation-in-part of U.S. Patent Application Serial No. 12/856,336, filed on Aug. The priority of the provisional patent application is hereby incorporated by reference in its entirety herein in its entirety in its entirety in its entirety.

The present invention relates generally to seamless tubular components and, more specifically, to the manufacture of high strength composite seamless tubular components from centrifugally cast corrosion resistant alloys using an extrusion metal forming process.

High-strength corrosion-resistant seamless tubular components have many commercial applications. For example, durable tubular components with high strength and resistance to failure in stress, corrosive and aggressive environments are used in oil well pipes (OCTG), and other types of tubular components are used to collect oil, gas or other fluids from wells. . These durable components are required due to the harsh well conditions in the well and/or the harsh environment surrounding the well. However, as wells become deeper, well conditions in the well may limit the choice of tubular components that can withstand such environments. Generally, temperatures and pressures in deeper wells are higher and may have corrosive atmospheres, such as hydrogen sulfide, carbon dioxide, chlorides, associated hydrocarbons, and/or acidic environments. Weight factor may also be a concern because more tubular components must be used in deeper wells And connect more tubular components together.

As a result, material selection criteria for such tubular components have become increasingly important as they may fail in relatively short periods of time due to stress corrosion cracking, corrosion pits, erosion wear and general wall damage ( For example, by reducing the burst resistance and crushing pressure of the assembly). At present, high strength corrosion resistant alloys have been used instead of conventional carbon steel for use in well tubular components under these harsh conditions. These tubular components are typically made of stainless alloys, duplex (austenitic-ferritic) stainless alloys and nickel-based alloys, such as the following alloys, such as alloys 28, 625, 718, 825, 925, G-3. , 050, C-276, 22Cr, 25Cr, Nickel 200, Monel 400 and Inconel 600. The failure resistance of components may be affected by many factors, including the chemical nature of the component materials, the nature and amount of alloying elements, and the dimensions of the components (such as bursting and crushing pressures with higher wall thickness tolerance). And the microstructure of the material that is affected by the manufacturing method of the component (eg, machining) and the nature of any heat treatment of the component.

Tubular components can be formed by a number of different manufacturing methods. One type of manufacturing process is casting, which means that the liquid material is typically poured into a mold and then the liquid material is cured. The mold contains a hollow cavity having the desired shape of the assembly. The solidified part is also referred to as a casting, and once the casting has cooled sufficiently, the casting is usually removed from the mold. Metals and alloys can be formed by this process. However, as-cast components typically include larger grain sizes and may contain casts such as porosity and non-metallic inclusions.

Centrifugal casting is somewhat different from this manufacturing method. During the centrifugal casting process, the mold is rotated about its axis at various speeds (eg, 300 rpm to 3000 rpm) while pouring molten material into the mold. The speed of rotation and the rate of material pouring vary with the materials used and the size and shape of the components being cast. When the molten material is poured into the rotating mold, the molten material is thrown to the outer wall of the mold, and the outer wall of the mold is usually kept at a temperature far lower than the temperature of the molten material, and the molten material at the outer wall of the mold is The cooling begins to solidify. In the vicinity of the outer wall of the mold, non-uniform nucleation occurs relatively quickly, and a fine equiaxed grain structure is generally obtained in the outer diameter of the assembly in the outer region adjacent to the mold. This rapid cooling effect of the mold causes directional solidification on the walls of the assembly. In each of the columnar grains parallel to the direction of the heat flow, the columnar regions begin to form in a dendritic growth direction. When such crystals encounter grains that begin to grow from the inner diameter of the component in the inner region, the growth of such crystals stops. Since the inner diameter of the assembly is in contact with air, the rate of solidification in the inner zone is much lower than the rate of solidification in the outer zone, resulting in coarser grains in the inner diameter than in the intermediate or outer diameter of the component. Thus, centrifugal casting typically produces a finer grain structure with finer grain outer diameter than conventional casting, but typically has more impurities and inclusions in the inner diameter.

However, the resulting centrifugal casting assembly presents many challenges to the subsequent metal forming process due to its different grain sizes in each zone and its radially oriented columnar grain structure. Due to these difficulties, casting and centrifugal casting components often undergo subsequent thermal or thermoforming manufacturing processes that are performed above the recrystallization temperature of the material; or to undergo a process between metal forming processes. Multiple annealing steps. However, mild thermal forming processes affect the mechanical properties and dimensional accuracy of the components, making it difficult to meet stringent tolerance requirements. Additionally, centrifugal casting components have not been approved for applications where internal pressure is high or corrosive and/or aggressive products are present, such as in environments where OCTG components are used. Centrifugal casting processes tend to produce microstructures with undesired porosity that cause crack initiation sites. The centrifugal casting assembly can also exhibit separation of solute alloying elements into a Laves phase and a carbide phase, depending on the speed of the mold used during casting. Microstructural results indicate that the major crack or fracture path in centrifugal casting is often associated with the carbide phase or the Laves phase in the dendritic intergranular region. It is well known that alloy inhomogeneity results in a decrease in tensile and latent damage properties of the material at room temperature and elevated temperatures. One of the major problems with centrifugally cast components is the non-uniform microstructure over the entire cross-section of the wall thickness. Stripe structure makes the material Physical and mechanical properties are degraded and cause delamination.

In accordance with one embodiment of the present invention, a method of making a seamless composite tubular product includes centrifugally casting a metal or alloy into a tubular workpiece having an inner diameter. The method then centrifugally casts a corrosion resistant alloy in the inner diameter of the tubular workpiece to form a composite tubular workpiece having an inner diameter and an outer diameter, the inner diameter of the composite tubular workpiece being formed by the corrosion resistant alloy and the composite The outer diameter of the tubular workpiece is formed from the metal or alloy. The method then uses a metal forming process to subject the composite tubular workpiece to a wall thickness reduction of at least about 25% at a temperature below one of the recrystallization temperatures of the composite tubular workpiece. The metal forming process includes radial forging, rolling, pel-rolling and/or flow forming.

In some embodiments, the method further includes centrifugally casting one or more metals or alloys in the inner diameter of the tubular workpiece prior to centrifugally casting the corrosion resistant alloy. The wall thickness reduction can be at least about 35% or at least about 50%. The 35% or 50% wall thickness reduction can include at least two reductions. The first reduction can be at least about 25% of the wall thickness reduction. The corrosion resistant alloy may comprise a stainless steel alloy, a titanium based alloy, a nickel based alloy, a cobalt based alloy and/or a zirconium based alloy. The method can further include removing material from the outer diameter of the composite tubular workpiece prior to subjecting the composite tubular workpiece to the reduction in wall thickness. The method can further include annealing the composite tubular workpiece after subjecting the composite tubular workpiece to the reduction in wall thickness. The method can further include subjecting the composite tubular workpiece to a wall thickness reduction of at least about 10% after annealing the composite tubular workpiece. The method can further include annealing, age hardening, and then annealing the composite tubular workpiece prior to subjecting the wall thickness to decrease. The method can further include forming a rifling on an inner diameter of one of the composite tubular workpieces. The metal forming process may further include providing at least two rollers having a displacement relative to each other in an axial direction relative to the composite tubular workpiece, and combining the axial force with one of the radial forces at the composite tubular workpiece The outer diameter of the composite tubular workpiece is pressed by the rollers at a temperature below one of the recrystallization temperatures such that the mandrel contacts the inner diameter and applies a circumferential compressive stress to the inner diameter of the composite tubular workpiece. The method can further include removing material from the inner diameter of the tubular workpiece prior to centrifugally casting the corrosion resistant alloy. The method can further include removing material from the inner diameter of the composite tubular workpiece prior to subjecting the composite tubular workpiece to the reduction in wall thickness. The wall thickness reduction can be from about 25% to about 75%. Embodiments can include a tubular assembly made in accordance with the method.

10‧‧‧Flow forming device

12‧‧‧ mandrel

14‧‧‧Tailstock

16‧‧‧ Roller

18‧‧‧Workpiece

19‧‧‧Removable carrier

20‧‧‧ axis

22‧‧‧ Direction

24‧‧‧ Direction

26‧‧‧ wall thickness

28‧‧‧ Length

30‧‧‧ Length

32‧‧‧压圈

34‧‧‧ head seat

36‧‧‧Nozzles

100‧‧‧ steps

110‧‧‧Steps

120‧‧‧Steps

A ₁ ‧‧‧ distance

A ₂ ‧‧‧ distance

K‧‧‧ angle

R ₁ ‧‧‧ distance

R ₂ ‧‧‧ distance

S ₀ ‧‧‧Wall thickness of the workpiece before the flow forming pass

S ₁ ‧‧‧Wall thickness of the workpiece after the flow forming process

V‧‧‧ direction

W‧‧‧ axis

X‧‧‧ Roller

Y‧‧‧ Roller

Z‧‧‧ Roller

The foregoing features of the present invention will be more readily understood by reference to the detailed description of the accompanying drawings in which: FIG. 1 illustrates a process of making a seamless composite tubular product in accordance with an embodiment of the present invention; A macroscopic photograph of a cross-sectional view of a centrifugally cast tube prior to cold working according to an embodiment of the present invention; and FIG. 3 is a longitudinal sectional view of a centrifugally cast stainless steel tube prior to cold working according to an embodiment of the present invention Photomicrograph; FIG. 4 is a photomicrograph showing a longitudinal cross-sectional view of a centrifugally cast stainless steel tube prior to cold working according to an embodiment of the present invention; FIGS. 5A and 5B are respectively shown in FIG. A photomicrograph of the as-cast microstructure in the inner and outer regions of the centrifugally cast tube; FIG. 6 schematically illustrates an illustrative flow forming device in accordance with an embodiment of the present invention; FIG. 7 schematically illustrates Side view of a workpiece undergoing a forward flow forming process of an embodiment of the present invention; FIG. 8 is a schematic side view of a workpiece undergoing a reverse flow forming process in accordance with an embodiment of the present invention; Figure 9 is a schematic perspective view of a roller in accordance with an embodiment of the present invention; Figure 10 is a schematic side view of a roller configuration in which a workpiece undergoes a forward flow forming process in accordance with an embodiment of the present invention Figure 11 is a diagram showing the residual circumferential stress distribution of a tubular component made of a superalloy material that has undergone a self-tightening process in accordance with an embodiment of the present invention; Figure 12 is a diagram showing an embodiment of the present invention in accordance with an embodiment of the present invention. A photomicrograph of a longitudinal section of a centrifugally cast stainless steel tube after flow forming; and FIGS. 13A and 13B show the flow-formed centrifugally cast stainless steel tube shown in FIG. 10 at 500 times magnification, respectively. Photomicrograph of the outer diameter region and the inner diameter region.

Various embodiments of the present invention provide a method of making a seamless composite tubular product from a centrifugally cast corrosion resistant alloy. The method entails centrifugally casting a metal or alloy, such as steel or a corrosion resistant alloy, to form an outer or shell layer in the centrifugal casting, and then using the shell as a mold to subsequently centrifugally cast a corrosion resistant alloy to form at least the two Composite tubular workpiece made of materials. The process then cold-processes the composite tubular workpiece, wherein a metal forming process, such as flow forming, is used to achieve a wall thickness reduction of at least about 25% to form the workpiece to a desired length, thickness, and/or shape. Two or more layers are bonded or coated together. Other metal forming processes can also be used, such as radial forging, rolling, and/or pilfer tube rolling. Preferably, the metal forming process includes a series of smaller and smaller reductions. Typically, in clinker such as small embryos or extrudates, if a smaller incremental flow forming pass is used, the material near the outer diameter of the component undergoes deformation sufficient to plastically deform the material, but the inner diameter is insufficient. Plastic deformation. Unacceptable, this condition causes the material to break. Surprisingly, it has been found that during the centrifugal casting of the corrosion resistant alloy, a series of smaller increments can be used and the larger radially oriented grain structures are rearranged in the longitudinal direction. This can Partly due to the presence of different grain structures in the inner and outer diameters of the centrifugally cast component. When at least 25% of the wall thickness is reduced, the outer and inner diameters of the workpiece are sufficiently plastically deformed. After this initial first reduction, a smaller increment reduction can also be used. Thus, embodiments allow the centrifugally cast composite workpiece to be formed into a high strength composite corrosion resistant assembly without undergoing a series of hot working and cold working tube thickness reductions. The details of the illustrative embodiments are discussed below.

Figure 1 illustrates a process for making a seamless composite tubular product in accordance with an embodiment of the present invention. The process begins in step 100 where a metal or alloy is centrifugally cast into a tubular workpiece to form a mold for another centrifugal casting. For example, any metal or alloy that can be centrifugally cast can be used for the outer layer or mold, such as steel or another corrosion resistant alloy. In step 110, a corrosion resistant alloy is centrifugally cast in the inner diameter of the tubular workpiece to form a composite tubular workpiece. Preferably, the second centrifugal casting is formed in the inner diameter of the first centrifugal casting in such a manner as to reduce or eliminate the formation of any intermetallic layers between the two castings. A suitable method for reducing or eliminating the formation of any intermetallic layer is known in the art, for example, in U.S. Patent No. 5,558,150, the disclosure of which is incorporated herein in its entirety. One or more other metals or alloys may also be centrifugally cast in the inner diameter of the tubular workpiece prior to centrifugal casting of the corrosion resistant alloy to form a multilayer composite tubular workpiece. Corrosion resistant alloys may include stainless steel alloys, titanium based alloys, nickel based alloys and/or zirconium based alloys (eg, alloys such as alloys 28, 316, 625, 718, 825, 925, G-3, 050, C-276, 22Cr, 25Cr, duplex stainless steel, Nitronic stainless steel, Nickel 200, Monel 400 and Inconel 600). Corrosion resistant alloys can be used in a variety of different applications. Thus, the listing of a particular alloy is merely intended to illustrate materials suitable for use in embodiments of the invention.

The centrifugal casting process uses various parameters (e.g., rotational speed, cooling rate, etc.) depending on the materials used and the dimensions of the parts being fabricated. For example, a 316 stainless steel material can be formed to have a thick sidewall. As mentioned above, before cold working Centrifugally cast tubular workpieces typically include three basic solidification zones, such as shown in FIG. As shown, the outer zone consists of a fine equiaxed grain structure near the outer diameter of the workpiece, the columnar zone consists of columnar grains oriented parallel to the radial direction, and the inner zone consists of a coarse equiaxed grain structure. . 3 and 4 are longitudinal and cross-sectional views, respectively, of a centrifugally cast 316 stainless steel tube prior to cold working, showing a radially oriented large columnar grain structure. In the composite tubular workpiece, an outer layer formed of a metal or an alloy and an inner layer formed of a corrosion resistant alloy may each include the three solidified regions.

For heat treatable or age hardenable materials, such as 410 stainless steel or 718 Inconel, an optional heat treatment can be applied to the workpiece after two centrifugal casting processes. For example, the workpiece can be age hardened and annealed one or more times. The phase transition in the heat treatment cycle can help reduce large columnar grains in the centrifugal casting prior to the use of any subsequent metal forming process. The heat treatment may include annealing, age hardening, and annealing to break and slightly refine the cast grain structure.

In a centrifugally cast composite tubular workpiece, the inner zone typically has a limited ductility compared to the remainder of the workpiece, which is due in part to the higher porosity present in this zone. For example, Figures 5A and 5B show photomicrographs of as-cast microstructures in the inner and outer regions, respectively. As shown, there is a higher volume fraction of pores in the inner zone than in the outer zone. One of the basic causes of porosity in metals and alloys is the escape of gases during solidification. During centrifugal casting, when molten material is poured into a rotating mold, bubbles may form in the material. Because of the low density of these bubbles, they experience lower centrifugal forces than the melt and will tend to accumulate in the inner zone on the inner diameter of the centrifugal casting assembly. The unevenness of ductility between the three zones introduces risk factors during the subsequent processing stages. Therefore, the amount of deformation experienced by each zone needs to be considered during the design of the processing stage to maintain a uniform quality along the width of the tube in the final product.

Returning to the process of Figure 1, in step 120, using a metal forming process to compound The tubular workpiece experiences a wall thickness reduction of at least 25% at a temperature below the recrystallization temperature of the composite tubular workpiece. Optionally, the material can be removed from the inner diameter of the composite tubular workpiece by any known removal process, such as machining or honing. While the remainder of the discussion will be made in the context of using flow forming as a metal forming process, the discussion of flow forming is merely illustrative and is not intended to limit the scope of the various embodiments. Thus, the metal forming process may include applying a pressing force to reduce the inner and outer diameters of the tubular workpiece to obtain other metal forming processes for reducing the wall thickness of the assembly, such as rolling, radial forging, and Pierre format.

Flow forming is a metal forming process used to make precise, thin-walled, cylindrical components. Flow shaping is typically performed by pressing the outer diameter of the cylindrical workpiece against the inner rotating mandrel using a combination of axial, radial and tangential forces from two or more rollers. The material is extruded beyond its yield strength, resulting in plastic deformation of the material. As a result, the outer diameter and wall thickness of the workpiece are reduced while their length is increased until the desired geometry of the assembly is achieved. Flow forming is a cold forming process. Although self-plastic deformation produces adiabatic heat, the workpiece, mandrel, and rollers are typically spread over a cooled coolant to dissipate the heat. This ensures that the material works well below its recrystallization temperature. As a cold forming process, flow forming increases the strength and hardness of the material, texturing the material, and generally achieves mechanical properties and dimensional accuracy that are closer to the requirements than any warm or hot forming manufacturing method known to the inventors.

Two examples of flow forming methods are forward flow forming and reverse flow forming. In general, forward flow shaping can be used to form a tube or assembly (eg, a closed cylinder) having at least one closed or semi-closed end. Reverse flow forming can generally be used to form a tube or assembly having two open ends (eg, a cylinder having two open ends). In some cases, a combination of forward flow shaping and reverse flow shaping can be utilized to successfully achieve the desired geometry. Typically, forward flow forming and reverse flow forming can be performed on the same flow forming machine by replacing the necessary tools.

FIG. 6 schematically illustrates an illustrative flow shaping device 10 in accordance with some embodiments of the present invention. In this case, the flow shaping device 10 is configured for forward flow shaping. The flow forming device 10 includes a mandrel 12 for holding a cylindrical workpiece 18, a tailstock 14 for securing the workpiece 18 to the mandrel 12, and two or more rollers for applying a force to the outer surface of the workpiece 18. 16 and a movable carrier 19 coupled to the roller 16. As shown in Figure 6, the rollers 16 can be angled equidistant from one another relative to the central axis of the workpiece 18. Roller 16 can be hydraulically driven and CNC controlled.

Figure 7 shows a side view of workpiece 18 undergoing a forward flow forming process. During this process, the workpiece 18 can be placed on the mandrel 12 with the closed or semi-closed end of the workpiece facing the end of the mandrel 12 (on the right side of the mandrel, as shown in Figure 6). The workpiece 18 can be secured against the end of the mandrel 18 by the tailstock 14 by, for example, hydraulic forces from the tailstock 14. The mandrel 12 and the workpiece 18 are then rotatable about the axis 20 while the roller 16 is moved into a position in contact with the outer surface of the workpiece 18 at a desired location along the length of the workpiece 18. The headstock 34 rotates or drives the mandrel 12, and the tailstock 14 provides additional assistance to rotate the mandrel 12 such that the long mandrel 12 rotates properly.

The carrier 19 can then move the roller 16 along the workpiece 18 (as shown in Figure 6, traveling from right to left), generally in the direction 24. Roller 16 can apply one or more forces to the outer surface of workpiece 18 to reduce its wall thickness 26 and its outer diameter, for example, using a combination of controlled radial, axial, and tangential forces. One or two nozzles 36 may be used to spray coolant onto the rollers 16, the workpiece 18, and the mandrel 12, but more nozzles may be used to dissipate the adiabatic heat generated when the workpiece 18 experiences a greater amount of plastic deformation. The mandrel 12 may even be immersed in a coolant (not shown), such as in a trough device, such that the coolant collects and concentrates on the mandrel 12 to keep the workpiece 18 cool.

The roller 16 may be capable of compressing the outer surface of the workpiece 18 with sufficient force to cause the material to plastically deform and move or flow in a direction 22 generally parallel to the axis 20. The roller 16 can be located at any desired distance from the outer diameter of the mandrel 12 or the inner wall of the workpiece 18. The length along the workpiece 18 can be a constant or varying wall thickness 26, as shown in FIG. Length 28 represents the portion of workpiece 18 that has undergone a flow forming process, while length 30 is the deformed portion. This process is referred to as "forward flow forming" because the deformed material flows in the same direction 22 as the direction 24 in which the rolls move.

In reverse flow forming, the flow forming device can be configured in a manner similar to that shown in Figure 6, but using a drive ring 32 instead of a tailstock 14 to secure the workpiece 18 to the mandrel 12. As shown in FIG. 6, the pressure ring 32 is located near the headstock 34 at the other end of the mandrel 12. Figure 8 shows a side view of a workpiece undergoing a reverse flow forming process. During this process, the workpiece 18 can be placed on the mandrel 12 and pushed all the way to the compression ring 32 at one end of the mandrel 12 (as shown in Figure 6, on the left). The roller 16 is movable into a position in contact with the outer surface of the workpiece 18 at a desired position along the length of the workpiece 18. The carrier 19 can then be moved toward the press ring 32 (as shown in Figure 6, in a right-to-left direction) to apply a force to the workpiece 18. This force can push the workpiece 18 into the press ring 32 where the workpiece 18 can be captured or secured by a series of serrations or other securing members on the face of the press ring 32. This allows the mandrel 12 and workpiece 18 to rotate about the axis 20 while the roller 16 can apply one or more forces to the outer surface of the workpiece 18. The material is plastically deformed and moves or flows in a direction 23 generally parallel to the axis 20. Similar to forward flow forming, the roller 16 can be positioned at any desired distance from the outer diameter of the mandrel 12 or the inner wall of the workpiece 18 to create a wall thickness 26 that can be constant or varied along the length of the workpiece 18. Length 28 represents the portion of workpiece 18 that has undergone a flow forming process, while length 30 is the deformed portion. When the workpiece 18 is machined, the workpiece 18 extends away from the press ring 32 along the length of the mandrel 12. This process is referred to as "reverse flow forming" because the deformed material flows in a direction 22 opposite the direction 24 in which the rolls move.

In addition to flow forming the part on a smooth mandrel to create a smooth inner diameter of the flow-formed tube, a peg or twist line can be formed into the bore of the flow-formed tube. This can be achieved by constructing the outer surface of the mandrel 12 to flow the workpiece into This is achieved by applying a twist, groove, notch or other configuration to the inner surface of the workpiece. For example, the mandrel can be constructed to have a spiral, straight, periodic, or other desired ridge on its surface. After the final flow forming pass is completed, the ridges leave turns, grooves, notches, and/or other configurations in the inner surface of the workpiece. Alternatively, after the flow forming process is completed, the inner surface of the workpiece can be lined and/or otherwise configured, for example, by appropriate machining of the inner surface of the workpiece.

When the material is plastically deformed and trapped/compressed onto the hard mandrel with the setting of the rotating roller, a large wall thickness reduction can be achieved at one time. In the process of centrifugally casting a corrosion-resistant alloy, if less than 20% of the wall thickness is reduced per flow forming, the outermost portion of the workpiece may be plastically deformed, but the material closest to the inner mandrel may not have sufficient plasticity. Deformed and the material may be catastrophically torn during processing. However, if an excessively large wall thickness is used in one pass (eg, greater than 75% or possibly even as low as 65%), the workpiece may not be able to be processed in an acceptable manner. The flow forming process does not move the material significantly and the inner diameter forms a rough texture. Therefore, it was found that a certain amount of wall thickness reduction was required at the first pass and a smaller reduction was used after the first pass if needed. When at least 25% of the wall thickness is reduced, the outer and inner diameters of the workpiece are sufficiently plastically deformed. The flow forming process uniformly "fines" the grain size and rearranges the microstructures relatively evenly in a longitudinal direction parallel to the centerline of the flow-formed tube. The flow forming process can be performed in one or more flow forming passes. When two or more passes are used, preferably the first pass is greater than the subsequent pass and the wall thickness is reduced by at least 25%. For example, for a wall thickness reduction of 35% using more than one pass, the wall thickness of at least 25% for the first pass may be reduced and the wall thickness may be reduced for 10% for the second pass. In another example, for a wall thickness reduction of 50% using more than one pass, the first pass may have a wall thickness reduction of at least 25%, and the second pass may have a wall thickness reduction of 15%. And the wall thickness of 10% can be reduced in the third pass. Better Ground, in one pass, the wall thickness reduction range is from about 25% to about 75%.

For a certain degree of cold working, the hardness and tensile strength of the material increase, while the ductility and impact value decrease. In addition, the porosity of the casting will be substantially eliminated via cold working deformation. Cold working also generally reduces the grain size of the material. When the material is cold worked, the microscopic defects nucleate in the deformed region. When a defect accumulates through deformation, the sliding or moving of the defect becomes more and more difficult to occur. This causes the material to harden. If the material undergoes excessive cold working, the hardened material may break. Thus, as each flow forming pass is made, the material becomes harder and less ductile, so a series of smaller and smaller reductions can be used after the first pass.

In addition to the increased biaxial strength and wear resistance, embodiments may also provide residual compressive stress induced by a self-tightening process at the inner diameter of the assembly. Self-tightening is a metal fabrication technique used on tubular components to provide increased strength and fatigue life to the tube by creating residual compressive stresses at the orifices. During a typical self-tightening process, pressure is applied within the assembly, causing the material at the inner surface to undergo plastic deformation while the material at the outer surface undergoes elastic deformation. The result is that after the pressure is removed, there is a distribution of residual stresses that provide residual compressive stress on the inner surface of the assembly. In an embodiment of the invention, in the final flow forming pass, the roller 16 can be configured such that the roller uses a combination of axial and radial forces to squeeze the outer diameter of the workpiece to allow sufficient force Pressing the inner diameter of the workpiece 18 against the mandrel 12 allows the inner diameter to be sufficiently plastically deformed to apply compressive stress to the inner diameter. This can be achieved by pulling the rollers sufficiently apart from each other. The flow forming process then presses the workpiece 18 against the mandrel 12 and clamps as compared to when the workpiece 18 is only released from the mandrel 12 or bounces back from the mandrel 12 (this typically occurs during a standard flow forming process). Mandrel 12. In this manner, pressing the inner diameter against the mandrel 12 imparts a circumferential compressive stress to the inner diameter of the flow-formed component.

9 and 10 respectively show perspective and side views of a roller configuration in accordance with an embodiment of the present invention. Figure 9 shows a carrier that accommodates three flow forming rolls (shown as X, Y, and Z in Figure 10) that are movable along three axes (shown as X, Y, and Z axes) and They are positioned radially about the main axis, for example by 120° from one another. Although the figures show three rollers, the process can use two or more rollers. The independently programmable X, Y, and Z rollers provide the necessary radial force, while the W-axis right-to-left programmable feed motion applies axial force. Each of the rollers may have a particular geometry to perform its particular function during the forming process. Additionally, the positions of the rollers 16 can be staggered relative to one another. The amount of staggering can vary and can be based on the initial wall thickness of the workpiece and the amount of wall thickness desired to be reduced in a given flow forming pass. For example, as shown in Figure 10, S _o shows the wall thickness of the workpiece before a given flow forming pass, and S ₁ shows its wall thickness after the flow forming process, with roller 16 along v Move in direction. The rollers 16 may be axially offset along the axial direction of the workpiece 18 (shown as the W-axis in Figure 9) and may be radially offset (along the X, Y and Z axes) relative to the centerline or inner diameter of the workpiece, preferably To apply a relatively uniform squeeze to the outside of the workpiece 18. For example, as shown in FIG 10, along the axial direction of the workpiece 18, the roller displacement or X may be separated by a distance A, and Y ₁ and the roller of the roller may be spaced a distance Z A _2. Similarly, the roller X can be radially displaced from the inner diameter of the workpiece by a distance S ₁ which is the desired wall thickness of the workpiece 18 after a given flow forming pass, the roller Y being radially displaceable by a distance R ₁ and the roller Z can be displaced radially by a distance R ₂ . As shown, once the amount of axial misalignment has been determined, the angle K can be used to help determine the amount of radial offset.

The further apart the rollers X, Y and Z are from each other, the greater the distortion of the spiral applied to the grain structure of the workpiece. Lubricant should be used between the inner diameter of the workpiece 18 and the mandrel 12 to reduce the problem of the workpiece 18 being caught or clamped to the mandrel 12 during this process. In this manner, the circumferential compressive stress applied to the assembly will reduce the likelihood of crack cracking and slow the growth rate of any crack that can crack on the inner diameter of the assembly, effectively improving the fatigue life of the tubular assembly. One benefit of this process is that the amount of compressive stress applied to the inner diameter can vary along the length of the tube depending on the roller configuration. For example, the rollers can be configured such that the compressive stress is only Apply a portion of the tube, for example, one end or the middle of the tube.

Figure 11 is a graph showing the residual circumferential stress distribution of a tubular component made of a superalloy material that has undergone a self-tightening process. As shown, three tubular workpieces made of L-605 material are formed, and according to an embodiment of the invention, the wall thickness of each workpiece is reduced to approximately 61%, 30%, and 20%, respectively. The wall thickness is reduced. In this case, the final dimensions of the three samples are about one inner diameter and a wall thickness of about 0.100-0.150". As shown in Figure 11, each workpiece exhibits residual compressive stress at its inner surface, where The depth measured in the samples still senses a small residual compressive stress in the workpiece. 20% of the workpiece with reduced wall thickness is 61% smaller than the wall thickness of the workpiece at the inner surface (for example, within the distance) The surface 0 depth exhibits a high residual circumferential stress, but 61% of the higher wall thickness reduction than 30% or 20% of the workpiece exhibits within the workpiece (eg, depth of about 5-40×10 ^-3吋) Large compressive stress.

Figure 12 is a photomicrograph showing a longitudinal section of a centrifugally cast 316 stainless steel tube subjected to a flow forming process. The sample was etched to show the grain structure. The outer diameter of the assembly is shown at the top of Figure 12 and the inner diameter is shown at the bottom. 13A and 13B are photomicrographs showing the outer diameter region and the inner diameter region of a flow-molded centrifugally cast 316 stainless steel tube at 500 times magnification, respectively. As shown, the amount of cold work experienced by the grain structure in the two regions is significantly different. In the outer diameter, the grain structure is more and flatter than the inner diameter, wherein the grains are substantially aligned in a longitudinal direction parallel to the centerline of the flow-formed component. In the inner diameter, the grain structure is less deformed than the outer diameter, wherein the grains have a grain flow that is slightly angled toward the radial direction. The outer diameter of the centrifugally cast flow-formed assembly also exhibits a hardness property that is significantly different from the inner diameter. The hardness near the outer diameter was measured as the hardness grade of Rockwell C 39-42, and the hardness near the inner diameter was Rockwell C 26-29.

After one or more flow forming passes, the assembly may undergo additional post processing, such as heat treatment. As is known to those skilled in the art, materials that have been hardened by cold working are available. Softened by annealing. Annealing can release stress, allow grain growth, or restore the original properties of the alloy, depending on the temperature and duration of the heat treatment used. Ductility can also be restored by annealing. Thus, after heat treatment, the assembly can undergo one or more additional flow forming passes without breaking.

As mentioned above, metal forming may include other cold working processes other than flow forming, such as pel-rolling, radial forging, and/or rolling. As is known to those skilled in the art, in the Pil format rolling process, the tubular assembly is rotated and the tubular assembly is reduced by forging and progressively extending the tube over a fixed conical mandrel to reduce the tube. . Two rollers or dies (each having a semi-circular recess extending in a circumferential direction) are joined from above and below the tube and roll back and forth on the tube (transfer length) while the fixed conical mandrel is held The center of the finished tube. At the beginning of the stroke or transfer, the circular cross section formed between the grooves of the two opposing rolls corresponds to the diameter of the tube and the thickest portion of the mandrel. As the mold moves forward on the tube, the area of the circular cross section decreases until the end of the transfer length corresponds to the outer diameter of the finished tube and the inner mandrel diameter corresponds to the inner diameter of the finished tube. Produces a finished tube with a longer length, a smaller outer diameter and a smaller inner diameter. As is known to those skilled in the art, the radial forging process can include four hammerheads that are moved in and out and hammered on the mandrel. The driver and the counter holder move the workpiece over the mandrel and into the hammerhead of the reciprocating motion. As is known to those skilled in the art, the rotary die forging process can include a plurality of dies that rotate as a unit within the stationary housing as the workpiece is pushed over the mandrel and into the die of the upset/die forged material.

While the above discussion discloses various exemplary embodiments of the present invention, it will be apparent to those skilled in the art that various modifications of the advantages of the invention may be made without departing from the true scope of the invention.

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Claims (20)

A method of manufacturing a seamless composite tubular product, the method comprising: centrifugally casting a metal or alloy into a tubular workpiece having an inner diameter; centrifugally casting a corrosion resistant alloy in the inner diameter of the tubular workpiece to form a composite tubular workpiece having an inner diameter and an outer diameter, the inner diameter of the composite tubular workpiece being formed by the corrosion resistant alloy and the outer diameter being formed by the metal or alloy; and using the metal forming process to cause the composite tubular workpiece to be The composite tubular workpiece undergoes a wall thickness reduction of at least about 25% at a temperature below one of the recrystallization temperatures, including radial forging, rolling, pel-rolling, flow forming, or a combination thereof. The method of claim 1, further comprising centrifugally casting one or more metals or alloys in the inner diameter of the tubular workpiece prior to centrifugally casting the corrosion resistant alloy. The method of claim 1, wherein the wall thickness is reduced to at least about 35% and includes at least two reductions, wherein the first reduction is at least about 25% of the wall thickness is reduced. The method of claim 1 wherein the wall thickness is reduced to at least about 50%. The method of claim 4, wherein the at least about 50% reduction in wall thickness comprises at least two reductions, wherein the first reduction is at least about 25% of the wall thickness reduction. The method of claim 1, wherein the corrosion resistant alloy comprises a stainless steel alloy, a titanium based alloy, a nickel based alloy, a cobalt based alloy or a zirconium based alloy. The method of claim 1, further comprising removing material from the outer diameter of the composite tubular workpiece prior to subjecting the composite tubular workpiece to the reduction in wall thickness. The method of claim 1, further comprising annealing the composite tubular workpiece after subjecting the composite tubular workpiece to the reduction in wall thickness. The method of claim 8, further comprising annealing the composite tubular workpiece The composite tubular workpiece is then subjected to a wall thickness reduction of at least about 10%. The method of claim 1, wherein the metal forming process is radial forging. The method of claim 1, wherein the metal forming process is rolling. The method of claim 1, wherein the metal forming process is a Piel format tube. The method of claim 1, wherein the metal forming process is flow forming. The method of claim 1, further comprising annealing, age hardening, and then annealing the composite tubular workpiece prior to subjecting the wall thickness to decrease. The method of claim 1, further comprising forming a meander line on an inner diameter of one of the composite tubular workpieces. The method of claim 1, wherein the metal forming process comprises: providing at least two rollers having a displacement relative to each other in an axial direction relative to the composite tubular workpiece; and using one of an axial force and a radial force in the Pressing the outer diameter of the composite tubular workpiece with the rollers at a temperature below the recrystallization temperature of the composite tubular workpiece such that the mandrel contacts the inner diameter and applies a circumferential direction to the inner diameter of the composite tubular workpiece Compressive stress. The method of claim 1, further comprising removing material from the inner diameter of the tubular workpiece prior to centrifugally casting the corrosion resistant alloy. The method of claim 1, further comprising removing material from the inner diameter of the composite tubular workpiece prior to subjecting the composite tubular workpiece to the reduction in wall thickness. The method of claim 1, wherein the wall thickness is reduced from about 25% to about 75%. A tubular component manufactured according to the method of claim 1.